The invention relates to keyboards as used, for example, in typewriters and computers.
It is known to provide loudspeakers in the keyboard of a computer. See, for example, U.S. Pat. Nos. 5,682,290 and 5,892,503. Space is at a premium in a keyboard and thus small loudspeakers must be used. However, conventional pistonic loudspeakers which are small enough to fit in such confined areas are generally incapable of producing an acoustic output with a wide frequency range such as is required for music or speech reproduction. Generally, the frequency range of such small loudspeakers is limited and thus the loudspeakers produce no more than a few simple tones, e.g. bell rings or bleeps.
It is an object of the present invention to provide a keyboard of enhanced acoustic functionality.
A keyboard comprising a bending wave loudspeaker comprising an acoustic radiator capable of supporting bending waves and a transducer mounted on the acoustic radiator to excite bending waves in the acoustic radiator to produce an acoustic output. The keyboard has a housing comprising a base, and support means for supporting the base above a work surface on which the keyboard is placed to define a gap between the base and the work surface. The bending wave loudspeaker is positioned in the housing so that its acoustic output is transmitted to a user via the gap between the base and the work surface. A user interface is carried by the housing above the base.
The loudspeaker may be a resonant bending wave mode loudspeaker comprising an acoustic radiator capable of supporting resonant bending wave modes and a transducer mounted on the acoustic radiator to excite resonant bending wave modes in the acoustic radiator to produce an acoustic output.
Such a resonant bending wave mode loudspeaker is described in WO98/09842 and other patent applications and publications, including U.S. patent application Ser. No. 08/707,012, filed Sep. 3, 1996 (incorporated herein by reference in its entirety), and may be referred to as a distributed mode loudspeaker.
The keyboard may comprise two loudspeakers, for example, a right and a left channel for stereo audio reproduction.
The keyboard may be a stand-alone device connected, for example, to a computer and monitor by an electrical cable or lead. The support means may be in the form of feet so that the base may be raised above the work surface on which the keyboard is placed. The whole, or alternatively only part, of the base may not be in contact with the rest surface when the base is raised on the feet.
The or each loudspeaker may be integrally formed with the base of the housing or may be a separate unit mounted in the base of the housing. The housing may further comprise side walls and a top defining with the base a cavity in the housing. Alternatively, the or each loudspeaker may be mounted inside the cavity. The or each loudspeaker may be supported on a mounting which may be either resilient or rigid. The base of the housing may be acoustically transparent to allow acoustic output from the loudspeaker to be transmitted to a user. The base of the housing may comprise a grid, a pierced panel or acoustically porous mounting.
One property of a distributed mode radiator is the diffuse nature of the propagation of acoustic output from the radiator. Accordingly, although the or each loudspeaker is located on the base of the housing or in the housing whereby sound is primarily transmitted though the base, the acoustic output circulates to the user. In particular, when the base is raised from the work surface, acoustic output may reflect off the work surface to the user.
There is generally positive interference between the reflected acoustic output and the radiated acoustic output which may improve the performance of the loudspeaker. In contrast, if a conventional loudspeaker were to be mounted in the base of the keyboard or inside the keyboard with the only sound radiation from the base of the keyboard, the reflected acoustic output and the radiated acoustic output would destructively interfere. Thus such an arrangement is unlikely to be possible with a conventional pistonic loudspeaker.
The properties of the acoustic radiator may be chosen to distribute the resonant bending wave modes substantially evenly in frequency. In other words, the properties or parameters, e.g. size, thickness, shape, material etc., of the acoustic radiator may be chosen to smooth peaks in the frequency response caused by xe2x80x9cbunchingxe2x80x9d or clustering of the modes. The resultant distribution of frequencies of the resonant bending wave modes may thus be such that there are substantially minimal clusterings and disparities of spacing of the frequencies.
In particular, the properties of the acoustic radiator may be chosen to distribute the lower frequency resonant bending wave modes substantially evenly in frequency. The distribution of resonant bending wave modes is less dense at lower frequency than at higher frequency and thus the distribution of the lower frequency resonant bending wave modes is particularly important. The lower frequency resonant bending wave modes are preferably the ten to twenty lowest frequency resonant bending wave modes of the acoustic radiator. For an acoustic radiator for use in a keyboard, the lower frequency resonant bending wave modes may all be below 3 kHz.
The resonant bending wave modes associated with each conceptual axis of the acoustic radiator may be arranged to be interleaved in frequency. Each conceptual axis has an associated lowest fundamental frequency (conceptual frequency) and higher modes at spaced frequencies. By interleaving the modes associated with each axis, the substantially even distribution may be achieved. There may be two conceptual axes and the axes may be symmetry axes. For example, for a rectangular acoustic radiator, the axes may be a short and a long axis parallel to a short and a long side of the acoustic radiator respectively. For an elliptical acoustic radiator, the axes may correspond to the major and minor axis of the ellipse. The axes may be orthogonal.
The transducer may be grounded or partially grounded. The transducer may be piezoelectric. The transducer location may be chosen to couple substantially evenly to the resonant bending wave modes. In particular, the transducer location may be chosen to couple substantially evenly to lower frequency resonant bending wave modes. In other words, the transducer may be mounted at a location spaced away from nodes (or dead spots) of as many lower frequency resonant modes as possible. Thus the transducer may be at a location where the number of vibrationally active resonance anti-nodes is relatively high, and conversely the number of resonance nodes is relatively low. Any such location may be used, but the most convenient locations are the near-central locations between 38% to 62% along each of the length and width axes of the panel, but off-central. Specific locations found suitable are at {fraction (3/7)}, {fraction (4/9)} or {fraction (5/13)} of the distance along the axes; a different ratio for the length axis and the width axis is preferred.
The acoustic radiator may have selected values of certain physical parameters which enable the acoustic radiator to sustain and propagate input vibrational energy in a predetermined frequency range by a plurality of resonant bending wave modes in a least one operative area extending transversely of thickness such that the frequencies of the resonant bending wave modes along at least two conceptual axes of the operative area are interleaved and spread so that there are substantially minimal clusterings and disparities of spacings of said frequencies, the acoustic radiator when resonating having at least one site at which the number of vibrationally active resonance anti-nodes is relatively high, and a transducer mounted wholly and exclusively on the acoustic radiator at one of said sites on the acoustic radiator, the transducer being capable of vibrating the acoustic radiator in the predetermined frequency range to couple to and excite the resonant bending wave modes in the acoustic radiator and cause the acoustic radiator to resonate and produce an acoustic output.
The acoustic radiator may be in the form of a panel. The panel may be flat and may be lightweight. The material of the acoustic radiator may be anisotropic or isotropic.
Thus, the acoustic radiator may be integrated in the keyboard without adding too much to the size and weight of the keyboard. In contrast, a conventional pistonic loudspeaker is likely to add too much to the size and weight of the keyboard to be practical.
The low form factor of a thin panel speaker makes it uniquely suited to a keyboard, which does not benefit from unnecessary thickness.
In one embodiment, the keyboard may be of the kind wherein the user interface has individual alphanumeric keys which may be electrically connected to associated display and/or printing means. The individual keys forming the keyboard may be supported on the housing, e.g. on a top of the housing. In another embodiment, the user interface may comprise a touchpad which may be supported on the base of the housing. The touchpad may be integral with one or more loudspeakers. Alternatively or additionally, the keyboard ay comprise a flat panel loudspeaker carrying touch pads to form the keys.
The keyboard may also incorporate data readout and/or display units to enhance functionality.